ATLANTIC CITY, N.J. — Internet gambling is slowly growing — but not expanding — after 2 1/2 years of online betting in the United States.

Online gambling revenue is increasing in at least two of the three states that currently offer it — New Jersey and Delaware. The third, Nevada, doesn’t report Internet revenue separately.

But a hoped-for wave of expansion has not happened as many states sit on the sidelines and assess the costs and benefits of the nascent industry.

“Internet gambling revenue in Delaware, Nevada and New Jersey badly missed initial forecasts, which themselves were overly aggressive,” said Chris Krafcik, research director for Gambling Compliance, which tracks gambling legislation nationwide.